DEVELOPING A NORTH AMERICAN MITOCHONDRIAL DISEASE CONSORTIUM This application addresses one broad Challenge Area, (07) Enhancing Clinical Trials (07-OD(ORDR)-102: Rare Disease Genetic Patient Registry. By most epidemiological studies, primary mitochondrial disorders, defined as inherited defects of the mitochondrial respiratory chain (RC), are rare diseases (<200,000 affected individuals in the US) due to primary mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Mitochondrial diseases are among the most clinically heterogeneous conditions because mitochondria are ubiquitous organelles and the expression of disorders due to mtDNA mutations depends on the proportion and tissue distribution of mutated mtDNAs. Thus, mitochondrial diseases are baffling to general practitioners, scary to patients and families, and generally misunderstood despite the organizational and teaching efforts of the patients advocacy group, the United Mitochondrial Disease Foundation (UMDF). Together with their rarity, the clinical and genetic heterogeneity of mitochondrial diseases has hindered natural history studies and rigorous clinical trials. In no other area of medicine is the need for a North American patient registry more critical. This application aims at establishing the infrastructure needed to launch a mitochondrial disease patient registry, biorepository, and a North American Mitochondrial Disease Consortium (NAMDC) with the support of UMDF. The NAMDC will feature advanced data management systems and statistical design capabilities provided by the Statistical Analysis Center (SAC) in the Department of Biostatistics at Columbia University. This structure will be the indispensable basis for future collaborative studies of epidemiology, natural history, therapeutic trials, as well as in-depth research on pathogenesis. As research on the mitochondrial role in human diseases progresses at a very rapid pace, the time is ripe for the establishment of a North American Mitochondrial Disease Consortium and patient registry, which will provide infrastructure for translational research and prepare the ground for rigorous natural history studies and therapeutic trials that are sorely needed for these generally devastating disorders.